Molecular Biology & Genetics · NEET PG Preparation Biochemistry
A 32-year-old man presents with progressive ataxia, nystagmus, and recurrent psychiatric disturbances. Genetic testing reveals an expansion of a trin…
Practice question from Molecular Biology & Genetics (NEET PG Preparation Biochemistry), with the correct answer and a step-by-step solution.
medium · MCQ · Q-75B511
A 32-year-old man presents with progressive ataxia, nystagmus, and recurrent psychiatric disturbances. Genetic testing reveals an expansion of a trinucleotide repeat (CAG) in the coding region of a specific gene. Which of the following best describes the molecular consequence of this specific trinucleotide expansion?
- A.Transcriptional silencing due to hypermethylation of CpG islands
- B.Gain-of-function toxicity due to polyglutamine tract expansion in the proteinCorrect answer
- C.Aberrant mRNA splicing leading to nonsense-mediated decay
- D.Impaired DNA mismatch repair causing microsatellite instability
Solution
The vignette describes Huntington disease or a similar polyglutamine (CAG repeat) disorder. CAG codes for glutamine. Expansion of CAG repeats in the coding region leads to a toxic gain-of-function via expanded polyglutamine tracts in the translated protein. Option A describes non-coding repeat expansions like fragile X syndrome (CGG) or Friedreich ataxia (GAA).
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